1. Field of the Invention
The present invention relates to a radio antenna apparatus provided with a controller for controlling a specific absorption rate (referred to as an SAR hereinafter), and a radio communication apparatus using the same radio antenna apparatus, such as a portable telephone, a car telephone, or the like.
2. Description of the Related Art
Recently, radio communication apparatuses such as a portable telephone and a car telephone have rapidly spread. The size of each of these radio communication apparatuses has been increasingly reduced year by year. Because of reduction in size of the radio communication apparatus, radio waves are radiated not only from an antenna but also from a housing of the radio communication apparatus. That is, electromagnetic waves are radiated from the entire radio communication apparatus.
A part of the electromagnetic wave radiated from the antenna and the radio communication apparatus is absorbed by a human body. A rate of a power quantity by which the human body absorbs the electromagnetic wave among the radiated radio waves are represented by an SAR. For the past few years, a guideline for suppressing the SAR is established and it is obligated to set the SAR to be equal to or smaller than a predetermined specified value as disclosed at, for example, a prior art document of Niels Kuster et al., “Energy Absorption Mechanism by Biological Bodies in the Near Field of Dipole Antennas Above 300 MHz”, IEEE Transactions on Vehicular technology, Vol. 41, No. 1, pp. 17–23, February 1992. For instance, since a portable telephone is used while being in the proximity to a head of the human body during telephone conversation, the head greatly absorbs the radio wave. In particular, since the housing is in contact with an ear or a cheek of the human body, the SAR may possibly be the highest on the housing.
FIG. 45 is a front view showing that the radio communication apparatus including a radio antenna according to a prior art is supported by the head of the human body. FIG. 46 is a perspective view showing an appearance of the radio communication apparatus shown in FIG. 45.
The radio communication apparatus shown in FIGS. 45 and 46 includes a whip antenna 1112 provided to extend upward from an upper portion of a housing 1111 of a rectangular parallelepiped shape, and an electrical conductor plate 1113 provided to be connected with the housing 1111 so as to be in parallel to a front surface (opposing to a user's face) opposite to a rear surface at the side of the whip antenna 1112. By connecting the conductor plate 1113 with the housing 1111, an electromagnetic wave in a direction of the human body, among those radiated from the radio communication apparatus in radiation directions indicated by an arrow 1113A and an arrow 1113B, can be shielded, and the SAR caused by the radio wave can be reduced (See, for example, U.S. Pat. No. 6,456,248).
However, the shape of the conductor plate 1113 according to the prior art is restricted, so that all the radio waves radiated from the radio communication apparatus cannot be shielded. Therefore, the effect of reduction of the SAR is insufficient only by shielding a part of the radio waves.